What is the ideal size of the state?

The British government is spending 50 per cent of GDP, but taking just 40 per cent in taxes. The coalition's aim is to close that gap over the next five years (still leaving a massive accumulated debt, by the way), partly by raising taxes and partly by cutting spending. The hope is that economic growth will keep the eventual figure closer to 40 per cent than to 50. What, though, is the optimum share?

The above video hazards an answer. The Rahn Curve is to state spending what the Laffer Curve is to taxation. Drawing on a mass of published data and economic models, it suggests that the ideal size of the state is between 15 and 25 per cent of GDP. Less than this and property rights start to look insecure; more and competitiveness suffers.

So, how do we go about getting there? Or even half way there? Any suggestions are welcome: the thread is open.